An optical resonator with an optical mode has a resonator block with and opening. At least one optical component is mounted on a holder that is positioned in the opening to locate the component in the mode of the resonator. The holder is contrained by the resonator block so that the orientation of the component in the plane of the resonator is substantially fixed by the opening. The component is simply aligned in the resonator by rotating the holder in the opening. The resonator block may also have a mirror reference surfaces that automatically aligns a mirror that is pressed against the surface. The resonator has a high degree of optomechanical assembly and facilitates initial component alignment and the interchange of optical components and mirrors.